Polypropylene film/adhesion promoter/metal laminate and its use for the production of packaging containers

Abstract

The present invention relates to polypropylene film-adhesion promoter-metal laminates, adhesion promoter used being polypropylene modified with carboxyl groups and/or anhydride groups. Polypropylene random copolymers of 90 to 99% by weight, preferably 93 to 99% by weight, of propylene and 1 to 10% by weight, preferably 1 to 7% by weight, of comonomers, having a molecular weight distribution M w :M n in the range from 2 to 10, preferably 3 to 6, and a melt flow index MFI 230° C./2.16 kg in the range of 1 to 20 g/10 min, preferably in the range from 4 to 15 g/10 min, are used for the production of the polypropylene film.

We claim: 
     
       1. A polypropylene film/adhesion promoter/metal laminate, comprising: a metal layer;   an adhesion promoter selected from the group consisting of polypropylene modified with carboxyl groups, polypropylene modified with anhydride groups, and mixtures thereof; and   a polypropylene film comprising polypropylene random copolymers of 90 to 99% by weight propylene and 1 to 10% by weight comonomers selected from the group consisting of C 2  and C 4  to C 12  monoolefins and mixtures thereof, wherein the polypropylene random copolymers have a molecular weight distribution M W  :M n  in the range from 2 to 10 and a melt flow index MFI 230° C./2.16 kg in the range from 1 to 20 g/10 min.   
     
     
       2. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the polypropylene film comprises polypropylene random copolymers of 1 to 4% by weight of ethylene and 99 to 96% by weight of propylene, based on the total weight of the monomers, having a molecular weight distribution M W  :M n  in the range from 3 to 6 and a melt flow index MFI 230° C./2.16 kg, in the range from 5 to 9 g/10 min. 
     
     
       3. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the polypropylene film comprises polypropylene random copolymers of 90 to 97% by weight of propylene, 2 to 5% by weight of ethylene and 1 to 6% by weight of but-1-ene, based in each case on the total weight of the monomers, having a molecular weight distribution M W  :M n  in the range from 3 to 6 and a melt flow index MFI 230° C./2.16 kg in the range from 4 to 8 g/10 min. 
     
     
       4. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the polypropylene film comprises a blend of the polypropylene random copolymer and up to 50% by weight of the polypropylene homopolymer based on the total weight of the polypropylene random copolymer and the polypropylene homopolymer in the film layer. 
     
     
       5. A polypropylene film/adhesion promoter/metal laminate according to claim 4, wherein the polypropylene homopolymer used has a molecular weight distribution M W  :M n  in the range from 3 to 6 and a melt flow index MFI 230° C./2.16 kg in the range from 4 to 15 g/10 min. 
     
     
       6. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the polypropylene film contains up to 0.5% by weight, based on the total weight of the polypropylene film, of compounds selected from the group consisting of erucamide, oleamide, and mixtures thereof, and up to 0.2% by weight, based on the total weight of the polypropylene film, of antiblocking agents. 
     
     
       7. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the adhesion promoter is a polypropylene random block copolymer grafted with 0.1 to 0.5% by weight, based on the total weight of the monomers, of maleic anhydride. 
     
     
       8. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the adhesion promoter is a polypropylene random copolymer grafted with 0.1 to 0.5% by weight maleic anhydride, and comprises 1 to 10% by weight comonomers selected from the group consisting of ethylene and C 4  to C 10  monoolefins and mixtures thereof, based on the total weight of the monomers. 
     
     
       9. Packaging containers comprising the polypropylene film/adhesion promoter/metal laminates according to claim 1. 
     
     
       10. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the adhesion promoter is a polypropylene random copolymer grafted with 0.2 to 0.4% by weight maleic anhydride, and comprises 1 to 10% by weight comonomers selected from the group consisting of ethylene and C 4  to C 10  monoolefins and mixtures thereof, based on the total weight of the monomers. 
     
     
       11. A polypropylene film/adhesion promoter/metal laminate according to claim 1, including SiO 2  as the antiblocking agent. 
     
     
       12. A polypropylene film/adhesion promoter/metal laminate according to claim 1, further comprising antioxidants and processing stabilizers. 
     
     
       13. A polypropylene film/adhesion promoter/metal laminate according to claim 1, wherein the polypropylene random copolymers are 93 to 99% by weight propylene and 1 to 7% by weight comonomers, and wherein the polypropylene random copolymers have a molecular weight distribution M W  :M n  in the range from 3 to 6 and a melt flow index MFI 230° C./2.16 kg in the range from 4 to 15 g/10 min. 
     
     
       14. A method for preventing crazing of a polypropylene film/adhesion promoter/metal laminate during formation of a packaging container, comprising the steps of: (a) forming a two-layer film by coextruding a polypropylene film and an adhesion promoter;   (b) covering a metal sheet with the coextruded film in such a way that the adhesion promoter layer comes into contact with the metal surface;   (c) laminating the metal sheet with the coextruded film to produce a polypropylene film/adhesion promoter/metal laminate; and   (d) forming the laminate into a packaging container having the polypropylene film as the inner coating surface; wherein the adhesion promoter is selected from the group consisting of polypropylene modified with carboxyl groups, polypropylene modified with anhydride groups, and mixtures thereof; and further wherein the polypropylene film includes polypropylene random copolymers of 90 to 99% by weight propylene and 1 to 10% by weight comonomers selected from the group consisting of C 2  and C 4  to C 12  monoolefins and mixtures thereof; and still further wherein the polypropylene random copolymers have a molecular weight distribution M w  :M n  in the range from 2 to 10 and a melt flow index MFI 230° C./2.16 kg in the range from 1 to 20 g/10 min.